1. Field of the Invention
This invention relates to a sleeve for abutting, aligning, and retaining opposed ferrules for use in an optical connector to be used for connecting optical fibers and a method for the production thereof.
2. Description of the Prior Art
Generally, the connecting part in an optical connector is composed of ferrules having connected thereto a sheathed optical fiber completed by coating the basic thread of an optical fiber with a sheath and a sleeve shaped like a hollow cylinder and adapted to, admit opposed ferrules in an aligned state. Particularly unlike the electric connector, the optical connector is required to ensure exact accord between the relative positions of two optical fibers to be connected. It, therefore, becomes necessary to fix an optical fiber in coincidence with the center of a ferrule having the outside diameter thereof and the inside diameter of the part thereof for allowing insertion of the basic thread of an optical fiber finished in respectively specified sizes and then insert a pair of such ferrules into a sleeve through the opposite ends thereof until mutual abutment, and center the axes of the optical fibers. As means for effecting this centering, the methods of the so-called adjusting type which rely on adjusting mechanisms to carry out fine adjustment and the methods of the no-adjusting type which are aimed at heightening the dimensional accuracy of ferrules and sleeves are available. Recently, the methods of the no-adjusting type have been predominating.
Heretofore, most of the ferrules which have been in popular use are those made of such ceramic substances as zirconia. By the same token, the sleeves which are made of such ceramic substances as zirconia have been in popular use.
Published Japanese Patent Application, KOKAI (Early Publication) No. (hereinafter referred to briefly as xe2x80x9cJP-A-xe2x80x9d) 6-27,348, for example, discloses a ceramic sleeve which is formed by providing a tubular body with ridges raised from at least three points on the inner wall surface of the tubular body and extended from one to the other end of the length of the tubular body. The ridge has an upper face formed in a concave circular arc included in a circle centering about the axis of the tubular body, namely a concave arcuate cross section facing the axis of the tubular body. The ridges and the inner wall surface of the tubular body are interconnected with gentle curves. The patent literature mentioned above further discloses a method for the production of the sleeve. This method comprises a step of manufacturing such a ceramic raw material as zirconia or alumina into a tubular body of such a geometric shape as described above, a step of calcining the resultant tubular body, and a step of polishing the upper faces of the ridges on the inner wall surface of the calcined tubular body. When the sleeve is a split type, the method further comprises a step of inserting a slit in the tubular body fresh from the polishing step throughout the entire length thereof in the longitudinal direction.
The ceramic sleeve constructed as described above is generally produced by subjecting the raw material first to primary forming in a cylindrical shape as by powder extrusion or injection molding and then to degreasing. and sintering treatments and machining works for grinding the outer surface of the tubular body and abrading the inner wall surface of the tubular body. The process of production, therefore, includes many steps and incurs an enormous cost inevitably. Further, since the raw material is brittle and rigid, the product brings about such problems as shedding chips and leaving the finish of surface polishing at the mercy of the grain size of crystals. Since the ceramic sleeve is rigid and deficient in elasticity, the ridges raised from the inner wall surface of the sleeve tend to inflict scratches on the outer faces of the ferrules and the sleeve and the ferrules, on repeating their mutual attachment and detachment, tend to backlash possibly to the extent of inducing a deviation from the axial alignment of the optical fibers. The ceramic substance, therefore, is not perfectly fit as a material for the sleeve in the optical connector which is prone to frequent attachment and detachment of the ferrules.
Further, since the ceramic sleeve inevitably contracts when it is sintered subsequently to the primary formation, it must be ground to prescribe dimensions by all means. When the ridges are formed as extended in the longitudinal direction on the inner wall surface of the tubular body, therefore, the upper faces of the ridges are ground in a concave arcuate shape along the axis of the tubular body as disclosed in JP-A-6-27,348 mentioned above. When these ridges are formed at three points on the inner wall surface of the tubular body, it is not the concave arcuate faces of the ridges but the opposite lateral edges of these faces in the longitudinal. direction that are actually exposed to contact with the outer peripheral surfaces of the ferrules which have been inserted into the sleeve. When the component ridges of the sleeve are exactly in agreement in size, therefore, the sleeve is fated to fix the ferrules in position in a state such that the opposite lateral edges (located at a total of six points) are held in contact with the outer surfaces of the ferrules. When the ridges involve a dimensional error, even if slightly, the contact occurs only at part of the points mentioned above. As a consequence, the possibility arises that the ridges will give rise to a deviation in contact and fixation at the points mentioned above in relation to the ferrules inserted into the sleeve opposite each other and the terminals of the optical fibers being connected consequently will inevitably deviate from their mutual axial alignment.
It is, therefore, an object of the present invention to provide a sleeve for optical connector ferrules which is capable of accurately abutting, aligning, and retaining opposed optical connector ferrules while incurring only sparingly such problems mentioned above as causing a deviation from axial alignment of the connected optical fibers and suffering the sleeves to shed chips.
A further object of the present invention to provide a method which, owing to the combination of a technique based on the conventional metal mold casting process or molding process with the quality of an amorphous alloy exhibiting a glass transition region, allows a sleeve for optical connector ferrules satisfying a predetermined shape, dimensional accuracy, and surface quality to be mass-produced with high efficiency by a simple process and, therefore, enables to omit or diminish markedly such machining steps as grinding and consequently provide an inexpensive sleeve for optical connector ferrules excelling in durability, strength, resistance to impact, and elasticity expected of the sleeve.
To accomplish the object mentioned above, the first aspect of the present invention provides a sleeve for abutting, aligning, and retaining opposed optical connector ferrules, which sleeve is characterized by being manufactured from an amorphous alloy instead of a ceramic material or metallic material which has been heretofore used.
The first embodiment of the sleeve for optical connector ferrules according to the present invention is characterized by being manufactured from an amorphous alloy possessing at least a glass transition region, preferably a glass transition region of a temperature width of not less than 30 K. In a preferred embodiment, the sleeve is characterized by being formed of a substantially amorphous alloy having a composition represented by the following general formula and containing an amorphous phase in a volumetric ratio of at least 50%:
xe2x80x83XaMbAlc
wherein X represents either or both of the two elements, Zr and Hf, M represents at least one element selected from the group consisting of Mn, Fe, Co, Ni, and Cu, and a, b, and c represent such atomic percentages as respectively satisfy 25xe2x89xa6axe2x89xa685, 5xe2x89xa6bxe2x89xa670, and 0 less than cxe2x89xa635.
The second embodiment of the sleeve according to the present invention, in view of the ease with which the optical connector ferrules and the sleeve used for abutting, aligning, and retaining the terminals of the ferrules succumb to deformation, is characterized by being manufactured from an amorphous alloy more susceptible of elastic deformation than the material for the optical connector ferrules lest the repetition of attachment and detachment of the sleeve and the ferrules should inflict injury on the ferrules or compel the ferrules to develop backlash.
The second aspect of the present invention, to give a sleeve a geometric shape fit for the purpose of abutting, aligning, and retaining opposed optical connector ferrules and to prevent the ferrules from being injured, consists in providing a sleeve characterized by having a tubular body provided at three points on the inner wall surface thereof with ridges extending from one to the other end of the tubular body in the longitudinal direction thereof, the ridges being so formed that the upper faces thereof may have an arcuate cross section which curves toward the axis of the tubular body.
The sleeve according to a preferred embodiment of the present invention is characterized by the fact that the tubular body mentioned above is provided throughout the entire length in the longitudinal direction thereof with such a slit as enables the optical connector ferrules to be elastically retained and preclude the occurrence of backlash even when the attachment and detachment of the sleeve and the ferrules are repeated.
Another aspect of the present invention consists in providing methods for the production of the sleeve for use with optical connector ferrules as mentioned above.
One mode of the methods is characterized by comprising the steps of melting an alloying material capable of producing an amorphous alloy in a melting vessel having an upper open end, forcibly transferring the resultant molten alloy into a forced cooling casting mold disposed above the vessel and provided with at least one molding cavity, and rapidly solidifying the molten alloy in the forced cooling casting mold to confer amorphousness on the alloy thereby obtaining the product made of an alloy containing an amorphous phase.
In a preferred embodiment of this method, the melting vessel is furnished therein with a molten metal transferring member adapted to forcibly transfer the molten alloy upward, the forced cooling casting mold is provided with at least two identically shaped molding cavities and runners severally communicating with the cavities, and the runners are disposed on an extended line of a transfer line for the molten metal transferring member.
Another method is characterized by comprising the steps of providing a vessel for melting and retaining an alloying material capable of producing an amorphous alloy possessing a glass transition region, providing a metal mold provided with at least one cavity of the shape of the product aimed at, coupling a hole formed in, for example, the lower or upper part of the vessel with a sprue of the metal mold, for example by disposing the metal mold beneath or on the vessel, applying pressure on a melt of the alloy in the vessel thereby enabling a prescribed amount of the melt to pass through the hole of the vessel and fill the cavity of the metal mold, and solidifying the melt in the metal mold at a cooling rate of not less than 10 K(Kelvin scale)/sec. thereby giving rise to the product of an alloy containing an amorphous phase.
In any of the methods described above, as the alloying material mentioned above, a material capable of producing a substantially amorphous alloy having a composition represented by the aforementioned general formula: XaMbAlc, and containing an amorphous phase in a volumetric ratio of at least 50% is advantageously used.
Still another method of the present invention is characterized by comprising the steps of heating an amorphous material formed of the alloy represented by the general formula mentioned above until the temperature of a supercooled liquid region, inserting the resultant hot amorphous material into a container held at the same temperature, coupling with the container a metal mold provided with a cavity of the shape of the product aimed at, and forcing a prescribed amount of the alloy in the state of a supercooled liquid into the metal mold by virtue of the viscous flow thereof.